1. Field of the Invention
The present invention relates to a semiconductor package and a fabrication method thereof, and more particularly, to a semiconductor package with a heat sink and a fabrication method thereof.
2. Description of Related Art
Generally, a semiconductor package such as a flip-chip ball grid array (FCBGA) package is provided with a heat sink so as to efficiently dissipate heat generated by a semiconductor chip during operation. As disclosed by U.S. Pat. Nos. 5,311,402, 5,396,403, 5,931,222, 5,637,920, 5,650,918 and 6,011,304, such a heat sink can be attached to a substrate mounted with the semiconductor chip by adhesive or solder. With the heat sink contacting the semiconductor chip, heat generated by the semiconductor chip during operation can be efficiently dissipated. Generally, the surface area of the heat sink is greater than that of the semiconductor chip such that the semiconductor chip can be covered by the heat sink completely.
FIG. 1 shows a conventional flip-chip ball grid array semiconductor package with a heat sink. As shown in FIG. 1, a semiconductor chip 11 is mounted on a substrate 10 through a plurality of conductive bumps 17, and a heat sink 15 comprises a flat portion 150 and a supporting portion 151 extending from the flat portion 150. The heat sink 15 is mounted on the substrate 10 via the supporting portion 151 and by an adhesive 14. The semiconductor chip 11 is received in a receiving space defined by the flat portion 150 and the supporting portion 151 of the heat sink 15 in a manner that a non-active surface of the semiconductor chip 11 is adhered to the flat portion 150 of the heat sink 15 by a heat conductive adhesive layer 16. Therefore, heat generated by the semiconductor chip 11 during operation can be dissipated efficiently by the heat sink 15.
However, owing to big differences between coefficients of thermal expansion (CTE) of the heat sink, the substrate and the semiconductor chip, thermal stress and thermal deformation generated during a thermal cycle process of the semiconductor chip package can easily lead to warpage of the package, and even lead to detachment of the heat sink from the substrate and crack of the conductive bumps, thereby adversely affecting the quality of electrical connection between the semiconductor chip and the substrate. Particularly, according to an equation δ=α*L*Δt, wherein, δ represents total deformation, α represents coefficient of thermal expansion, L represents length, and Δt represents change in temperature, both the thermal stress and the thermal deformation are directly proportional to length. Thus, maximum thermal stress and thermal deformation usually occur to a corner of the heat sink 15.
To decrease the thermal stress arising from different coefficients of thermal expansion, an adhesive of a low Young's modulus, such as a silicone-base adhesive, is usually disposed between the heat sink 15 and the substrate 10 so as to absorb the heat stress. However, such an adhesive of a low Young's modulus fails to provide sufficient supporting strength to the heat sink 15. Instead, such an adhesive often leads to unevenness of the heat sink 15 and even affects the appearance of the semiconductor package and an ensuing assembly process. On the other hand, although an adhesive of a high Young's modulus provides sufficient supporting strength, such problems as detachment of the heat sink 15 from the substrate 10 and crack of conductive bumps 17 may still occur because of the thermal stress. Therefore, it often needs to take a large amount of time to find suitable adhesives for mounting heat sinks and chips of different sizes on a substrate, which thus increases fabrication time and fabrication cost.
Accordingly, there exists a strong need in the art for a semiconductor package with a heat sink and a fabrication method thereof to solve the drawbacks of the above-described conventional technology.